Magnetoelastic-Harmonic Stress Sensors With Tunable Sensitivity

A wireless and passive stress sensor was developed by measuring changes in the induced magnetic field of a magnetoelastic strip under varying force loadings. The magnetoelastic strip was made of an amorphous ferromagnetic alloy and was attached to a solid body at its two longitudinal ends to form a bridge-like structure. When subjected to a lateral loading, the bridge-like structure allows the magnetoelastic strip to deflect, creating a longitudinal stress and changing its magnetic property. To remotely monitor the force loading, an AC magnetic field is applied and the magnetic fields induced by the magnetoelastic strip are recorded at multiple frequencies of the excitation frequency (higher-order harmonic fields). Experimental results showed that the second-order harmonic field (at twice the excitation frequency) amplitude produced by the sensor increased with applied compressive stress. It was also illustrated that sensor sensitivity with applied stress could be controlled by changing the length of the magnetoelastic strip. Good repeatability and stability were demonstrated with the highest signal drift of 9.45% occurring at a 9.7 kPa compressive load. Furthermore, a theoretical model was developed and evaluated to show the correlation between mechanical loading and second-order harmonic fields. Potential applications of this wireless and passive sensor technology include the monitoring of pressure in sphincter of Oddi, aortic aneurysms, and knee joint prostheses.